The refugees, in a column stretching 22 miles from the Albanian borders, were turned back early Wednesday when Yugoslavia suddenly sealed off its borders with Albania and Macedonia.

They vanished – leaving a line of empty cars and abandoned tractors.

Reports from a handful of refugees who arrived since the borders were shut indicated they simply disappeared from the landscape.

“There were cars abandoned on the other side, with no people. We don’t know what happened to them, and I’m very, very worried because after such a large flow of people suddenly it stops,” said Sadako Ogata, the United Nations High Commissioner for Refugees.

Her agency had no estimate of the number of missing refugees, but the Organization for Security and Cooperation in Europe put it at 80,000.

NATO Secretary General Javier Solana said the Serbs probably turned the refugees back to use them as human shields “in case the alliance’s military action is concentrated more on the ground.”

State Department spokesman James Rubin agreed.

A senior NATO military officer said, “We already know that Serb police have been using Kosovar males, who were separated from their families, as protective shields. This is a cynical and inhumane way to behave, but frankly it would come as no surprise, given the recent history of Serb atrocities.”

Sir John Day, Britain’s air marshal, said NATO would “take every precaution” to avoid hitting ethnic Albanians if they were used, in effect, as human shields.

But he emphasized that “at the end of the day, the responsibility for their fate rests with Milosevic.”

With the airstrikes in Yugoslavia in their 16th day, U.S. officials offered cautious support for a Cypriot mission aimed at winning the release of three captured GIs.

“I would be for anything … that secured their release,” President Clinton said.

Spyros Kyprianou, the speaker of the Cypriot parliament and the country’s president from 1977 to 1988, flew to Belgrade last night to try to win the release of Andrew Ramirez, Christopher Stone and Steven Gonzales.

The soldiers were captured last month along the Yugoslavia-Macedonia border, reportedly by a band of peasant farmers angry with the NATO bombing campaign.

Rubin said that despite Kyprianou’s presence in Belgrade, the bombs would continue to fall.

“We did not agree … to any sort of cease-fire. We’re not going to make that kind of concession,” he said.

Even though Kyprianou is friendly with Milosevic, Vice Premier Vojislav Seselj seemed to rule out releasing the GIs.

“America is waging an undeclared war against Yugoslavia” so freeing the soldiers “is out of the question,” he said.

Although Serbian leaders insist they are honoring a cease-fire to mark the Orthodox Easter holiday, German Defense Minister Rudolf Scharping said more than 35 Kosovars were killed in two massacres.

“Near the town or village of Pastric a massacre has taken place in the last 24 hours, and near the village of Sopi 35 unarmed civilians were assassinated,” he said.

NATO airstrikes on roads and bridges in Kosovo are hampering the ability of Serbian forces to move around, said French journalists who entered western Kosovo yesterday with Kosovo Liberation Army fighters.

“We have attacked the nervous system. We have attacked the central system as well, that is to say a part of the brain that is conducting the operations,” said French Army Chief of Staff Gen. Jean-Pierre Kelche.

Western officials say the latest wave of air attacks are focused on Serbian police and army units scattered in rural areas of Kosovo.